Strength, water permeability and synergy of marble slurry powder and stone dust concrete

Sand extraction and the disposal of stone industry fines are pressing environmental burdens. Marble slurry powder and crushed stone dust have each been studied separately, but a coupled evaluation of the two wastes, with a quantitative synergy assessment and a multicriteria selection framework, has been missing. An 11-mix programme, varying marble slurry powder (0, 10% and 20% by mass of cement) and crushed stone dust (0%–100% replacement of sand) in nominal 1:2:4 concrete, is converted into a performance envelope. Fresh, mechanical and water transport properties were normalised against the control and combined through a multicriteria performance index. Among the mixes with complete data, 10% marble powder with 50% crushed stone dust gave the best balance: 28-day compressive strength reached 26.1 MPa, about 23% above the control, and the 7-day water permeability coefficient fell about 2.6-fold, an early-age indication requiring later confirmation. A synergy index is suggestive of a positive interaction, though not statistically confirmed, whereas 20% marble powder is not beneficial. The behaviour suggests a physical filler, packing and pore refinement mechanism rather than a pozzolanic reaction. Diverting both wastes into concrete offers strength, early-age permeability and resource substitution benefits for the material sources studied.